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was confirmed by the characterization of a stable adduct of leu-arg. Figure 10.9 shows the product-ion spectrum of this adduct. Loss of 4-methylpentanoic acid and leucine from the molecular ion (m/z 504) generated the product ions at m/z 391 and m/z 373, respectively. Loss of the N-terminal leuarg generated the C-terminal ion at m/z 269, and further loss of aminon-itrile (NH2-CN) generated the product ion at m/z 227. The product ion at m/z 135 corresponded to the 4-methoxybenzaldehyde portion of the molecule.

The formation of an electrophilic a,fi-unsaturated aldehyde intermediate was confirmed with the same methodology in the rat liver microsomal incubation of ticlopidine, an antiplatelet drug that causes severe hematological abnormalities. Figure 10.10 shows the product-ion spectrum and proposed fragmentation scheme of the trapped adduct. Loss of 4-methylpentanoic acid and leucine from the molecular ion (m/z 549) generated the product ions at m/z 436 and m/z 418 respectively. The product ion at m/z 288 corresponded to the molecular mass of leu-arg, and loss of leu-arg from the molecular ion generated the product ion at m/z 262. The product ion at m/z 125 corresponded to chloromethylbenzene.

Thiophene-2-3-epoxide intermediate may have been involved in the formation of the GSH adduct at m/z 524 (Figure 10.11). The GSH adduct at m/z 546

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